Now, I've been a father for 12 years, and I've signed a lot of birthday, valentines day, etc. cards "Dad", but this sending mail signed "Dad" is new, and it's sort of freaking me out. For the better part of the past 20 years, "Dad" around here generally referred to The Wife's father, as in my saying "Hon, your Dad called" or her saying "Dad sent The Girls something" or the like. I had a mini-version of this a month or so back when The Wife put a list of important phone numbers on the fridge and "Dad's Cell Phone" was up there, which I immediately assumed was my father-in-law's, until I realized that was my (usually turned off an in the bottom of my briefcase) cell.
Admittedly, this is a rather exclusive sub-set of my communications, but it just seems weird, at age 50, to be having to add another "signing identity" to the list of those I've used either all my life, or since e-mail/IRC (ala BTRIPP) has been around!